Biology subjects

Guan, Z.

Publications and source records attributed to Guan, Z..

At least 19 recordsLinked to original sources

bioRxiv2026

Oral Bacterial Translocation Promotes Lung Dysbiosis and Infection Risk after Spinal Cord Injury

Spinal cord injury (SCI) causes systemic pathophysiology that extends beyond the injured spinal cord. Respiratory infections remain a leading cause of death after SCI and can impair neurological recovery, yet the microbial source of these infections remains poorly defined. This study defined the onset and origin of pulmonary dysbiosis after SCI by testing whether commensal bacteria move to the lung from the gut or oral cavity. In a murine model, bacterial culture, 16S rRNA sequencing and source-tracking analyses showed that SCI rapidly increased lung bacterial burden and shifted the pulmonary microbiome toward an oral-like community. Gut-associated bacteria did not measurably reach the lung through lymphatic or vascular routes. Systemic antibiotics commonly used to treat infection failed to reliably reduce post-SCI lung bacterial burden. In contrast, oral and lung-directed antibiotic delivery reduced bacteria linked to post-injury dysbiosis more effectively. These findings identify the oral cavity as a proximal source of lung dysbiosis after SCI, and support route-specific strategies to prevent respiratory infection after SCI.

neuroscience↗

bioRxiv2026

Accumulation of Lipid Droplets in Microglia following Neonatal Brain Hypoxia-Ischemia

BackgroundHypoxic-ischemic encephalopathy (HIE) is a major cause of neonatal mortality and neurodevelopmental impairments. Following brain hypoxia-ischemia (HI), microglia face substantial metabolic stress; and upon phagocytosis, they become overloaded with lipids derived from engulfed dead neurons and myelin debris. It is unclear how microglia respond to and process the lipid cargo, and whether lipid accumulation may affect microglia function following neonatal HI. MethodsThe postnatal day 10 mice were subjected to HI using the Vannucci model. Lipid droplets (LD) were assessed by histology and immunofluorescent staining. Single-nucleus RNA sequencing (snRNA-seq) was performed using brain tissue from HI-injured and sham-operated mice at 72 hours after HI. LD-accumulating microglia (LDAM) were identified by a specific LD marker gene perilipin 2 (Plin2). Differential gene expression was analyzed between Plin2-positive and Plin2-negative microglia after HI. Human HIE brain sections were also examined for LD accumulation. The dynamic changes of PLIN2-expressing microglia and infiltrating monocyte-derived macrophages (MDM) at 24 hours, 72 hours and 7 days after HI were compared using flow cytometry. In addition, mouse BV2 microglia were subjected to oxygen-glucose deprivation (OGD) to study phagocytosis and cytokine expression. ResultsLipid droplets accumulated primarily in microglia after HI in neonatal mice and in human HIE brain. LD were not found in astrocytes or neurons. Plin2-expressing LDAM emerged as new microglia clusters after HI. Compared with microglia without LD, LDAM showed a distinct transcriptional profile with upregulation of genes linked to microglial activation, enhanced cholesterol and lipid processing, and a shift towards phagocytic and pro-inflammatory state. Blocking LD biogenesis reduced elevated phagocytosis and IL-1{beta} expression in BV2 cells following OGD. ConclusionOur study revealed that microglia accumulate lipid droplets as part of their metabolic responses to HI in the neonatal brain. Microglial lipid droplet formation is associated with a pro-inflammatory phenotype at early stage after HI, and increased phagocytosis in vitro. The lipid metabolic changes may regulate microglial function and influence HI outcomes.

neuroscience↗

bioRxiv2026

Telomeric G-Quadruplexes Formed by Six G-overhang Permutation Repeats

The single-stranded G-overhangs of vertebrate telomeres, composed of guanine (G)-rich hexanucleotide repeats, can adopt six register-dependent permutations: GGTTAG, GTTAGG, TTAGGG, TAGGGT, AGGGTA, and GGGTTA. Telomeric G-quadruplexes (G4s) formed by the first two repeat permutations, which are the most prevalent at human chromosome ends, have been largely overlooked. Here, G4 formation across all six permutations, each containing 4 to 9 repeats, are systematically investigated under varying cation conditions and molecular crowding environments. Our findings reveal that distinct repeat permutations yield markedly different G4 stabilities and folding topologies, which in turn modulate DNA polymerase activity. This expanded perspective on telomeric structural diversity provides new insights into telomere biology and suggests that multiple repeat patterns may cooperatively influence chromosome end protection and targeting.

biophysics↗

bioRxiv2026

Single-nuclear RNA sequencing reveals an ATF3-independent sensory-neuron program after surgical incision

BackgroundAcute postoperative pain is common and often treated with opioids, but which sensory-neuron changes are responsible for the peripheral drive of pain is poorly defined. Skin incision induces activating transcription factor 3 (ATF3), the canonical marker of nerve injury, in dorsal root ganglion (DRG) neurons, and ATF3 marks the neurons that remain hyperexcitable. Whether ATF3 is required for postoperative pain is unknown. MethodsAdult mice of both sexes underwent hind-paw plantar incision. Postoperative nociceptive behavior was compared between sensory-neuron-specific ATF3 conditional-knockout mice (AvilCre/+; Atf3fl/fl) and littermate controls using assays that probe distinct primary-afferent modalities (von Frey; Hargreaves; dynamic light touch) together with an operator-independent index of spontaneous injury behavior. Single-nucleus RNA sequencing of wild-type and ATF3-null DRG sensory neurons (naive and postoperative day 1) characterized the initiating injury program; transcription-factor-activity inference, RNAscope, and phospho-c-Jun immunostaining examined c-Jun; and the oral dual leucine zipper kinase (DLK) inhibitor GNE-3511, given at the time of incision, was tested behaviorally. ResultsIncision transiently induced ATF3 in a subset of DRG neurons, returning to baseline by day 14, in parallel with the two-week course of nociceptive behavior. Deleting ATF3 in sensory neurons did not change the onset or resolution of nociceptive behavior on any readout, in either sex, across mechanical, thermal, and tactile modalities. Single-nucleus profiling showed a broad surgery-responsive nociceptor program in which ATF3 was the most strongly induced gene, yet only 23% of surgery-responsive neurons expressed it. Without ATF3, the program was remodeled but not abolished, and transcription-factor-activity inference nominated c-Jun as a candidate ATF3-independent factor; incision induced c-Jun in vivo. Systemic inhibition of DLK, which activates c-Jun pathway, lowered c-Jun phosphorylation and reduced evoked nociceptive hypersensitivity. ConclusionsOur results indicate that ATF3 marks part of the injured sensory neuron but does not drive acute post-surgical nociceptive behavior, and that it is not required for the postsurgical pain behaviors across afferent modalities carried by molecularly distinct nociceptor classes. The underlying injury program is broader than ATF3 and is nominated to depend on c-Jun. Because DLK inhibition, given at the time of incision, reduced evoked hypersensitivity, we propose the DLK-JNK-c-Jun axis as a candidate perioperative non-opioid target, which will require further genetic validation.

neuroscience↗

bioRxiv2026

The DUF998 family protein DrmA modulates cationic glycolipid levels and the emergence of high-level daptomycin resistance in Enterococcus faecalis

Daptomycin resistance (DAP-R) in enterococci is associated with alterations in the membrane lipid composition. The membrane-bound protein MprF is responsible for the synthesis of amino acid-modified lipids in bacteria, and these modified lipids contribute to DAP-R in some Gram-positive pathogens. In enterococci, MprF synthesizes three lysine-modified lipids: the phospholipid lysyl-phosphatidylglycerol (Lys-PG), and the newly identified cationic glycolipids lysyl-diglucosyl-diacylglycerol (Lys-Glc2-DAG) and lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG). Given the recent discovery of cationic glycolipids in enterococci, we re-examined a collection of laboratory-evolved DAP-R E. faecalis to investigate whether these lipids contribute to DAP-R. We found that levels of Lys-Glc2-DAG were strikingly reduced in DAP-R variants with high-level resistance. The dramatic alterations in Lys-Glc2-DAG levels were temporally coupled with the emergence of loss-of-function mutations in the gene drmA, which encodes a DUF998 family protein of unknown function. DrmA is a membrane protein with six predicted transmembrane helices and is widely distributed among Gram-positive and Gram-negative bacteria, including plant and animal pathogens. Complementation of the DAP-R strains with wild-type E. faecalis drmA significantly lowered their DAP MIC, reversing their trajectory to high-level DAP-R. Using genetic and lipidomic approaches in the natively DAP-sensitive strain OG1RF, we conclusively linked drmA loss-of-function with significantly reduced Lys-Glc2-DAG levels as well as a small but significant increase in Lys-PG levels. Yet, drmA inactivation in OG1RF did not alter its DAP MIC. We conclude that drmA loss-of-function confers elevated DAP MIC on the background of preceding mutations in the DAP-R evolutionary trajectory, most likely mutations in cls1. The recurrence of drmA mutations in multiple studies underscores its importance in DAP-R evolution. Overall, our work identifies a role for the DUF998 family in cellular lipid homeostasis and confirms its significant role in the evolution of DAP-R.

microbiology↗

bioRxiv2026

Anionic bacterial sphingolipids increase membrane stiffness

Recent genetic and bioinformatic studies have led to the discovery that many bacterial species encode the genes required to produce sphingolipids. Shotgun lipidomic studies have identified numerous sphingolipid species with novel structures that do not exist in eukaryotic organisms. The impacts of these lipids on the biophysical properties of bacterial membranes have not yet been determined. In this study, we purify a novel anionic bacterial sphingolipid, ceramide phosphoglycerate (CPG), and investigate its effect on membrane zeta potential and bending stiffness. CPG and its precursor, ceramide 1-phosphate (C1P), are shown to increase the magnitude of the membrane zeta potential. These sphingolipids also increase the stiffness of these membranes, with CPG increasing rigidity more than C1P or ceramide. This work provides experimental and computational methods of lipid isolation and characterization that may be broadly applicable to a variety of uncharacterized bacterial sphingolipids. SIGNIFICANCEThe diversity of bacterial sphingolipids far exceeds those found in eukaryotes. However, the function and biophysical properties of these lipids are unknown. Characterization of these lipids is a challenge as they are not commercially available. In this study, we developed experimental methods to purify the anionic sphingolipid ceramide phosphoglycerate and incorporate it into liposomes for analysis. Furthermore, we built computational tools to determine the bending stiffness of sphingolipid-containing vesicles from thermal fluctuation data.

biophysics↗

bioRxiv2026

Visual gamma stimulation causes prolonged enhancement of low-frequency blood flow oscillations across cortical regions in mice

IntroductionGamma entrainment using sensory stimuli (GENUS) uses 40Hz-pulsed sensory stimuli to entrain neural activity in the gamma band (30-150Hz). However, the effect of GENUS on low-frequency vascular oscillations has not been fully explored. ObjectivesThe objective of this study is to elucidate the effect of GENUS on vasomotion in healthy mice and potential confounds for future application in disease studies. MethodsHead-fixed, awake C57Bl/6 mice (n=18; 9M 9F) aged between 18 to 60 weeks were subjected to white light of either 40Hz visual flicker (GENUS), or constant stimulus (control). Blood flow was imaged using laser speckle contrast imaging (LSCI) before, during, immediately after 1 hour of stimulus, and 30min after the stimulus termination. ResultsA linear mixed-effects model showed that GENUS enhanced the magnitude of 0.2-0.4Hz blood flow oscillations by 38% during stimulation and by 30% at 30 minutes after stimulation compared to control when controlled for age, sex, and other factors. The effect on vasomotion was distributed across many cortical regions not limited to visual areas and lasted beyond 24 hours post-stimulus. ConclusionThese results support the exploration of GENUS for increasing vasomotion in therapeutic contexts. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=186 SRC="FIGDIR/small/729102v1_ufig1.gif" ALT="Figure 1"> View larger version (67K): org.highwire.dtl.DTLVardef@1deee2eorg.highwire.dtl.DTLVardef@e71833org.highwire.dtl.DTLVardef@1e5c4f0org.highwire.dtl.DTLVardef@1e4832e_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2026

Structure-guided discovery and engineering of miniature CRISPR-Cas12m for epigenome editing

CRISPR-based epigenome editing represents a programmable strategy to precisely modulate gene expression, holding immense promise for therapeutic applications. However, the large size of the dCas proteins substantially impedes the delivery via adeno-associated virus (AAV) vectors. Here, through iterative bioinformatics analysis, structure-guided predictions, and functional assays, we identified and characterized PmCas12m, a novel miniature subtype V-M CRISPR-Cas12m. PmCas12m exhibited flexible 5-YTN-3 PAM-dependent recognition and robust double-stranded DNA binding properties, while lacking DNA cleavage activity, thus positioning it as an ideal tool for epigenome editing. Cryogenic electron microscopy (cryo-EM) structures of PmCas12m unveiled its unique molecular mechanism of DNA binding facilitating interference. Guided by these structural insights, we employed deep mutational scanning (DMS) and protein engineering to develop xCas12m, a hypercompact variant with highly potent and specific epigenome editing capabilities in human cells. We further constructed the xCas12m-CRISPRoff platform in a single AAV vector, which achieved durable epigenetic silencing and effective inhibition of hepatitis B virus (HBV) infection in a mouse model. Collectively, these findings establish xCas12m as a versatile epigenome editing platform with transformative potential for treating diseases, paving the way for clinical translation of epigenetic therapies.

bioengineering↗

bioRxiv2026

Disease-causing mutations in Synaptotagmin can act via dominant-negative, gain-of-function or haploinsufficient mechanisms

Members of the Synaptotagmin (SYT) family of synaptic vesicle (SV) proteins contain two Ca2+ binding C2 domains (C2A and C2B) that regulate the timing and probability of SV fusion. Recently, dominant mutations in SYT1, present at most CNS synapses, and SYT2, abundant in the PNS, have been found to cause human neurological diseases. Most pathogenic alleles localize to the C2B Ca2+ binding pocket, although mutations outside of this region have been identified. Here we report the effects of a large array of disease-associated human SYT point mutations on synaptic transmission using the Drosophila model to define their mechanism of action. Mutations in the C2B Ca2+ binding pocket were the most severe and acted in a dominant-negative manner to decrease evoked release. Indeed, mutations in the C2B Ca2+ binding pocket were a privileged site for dominant-negative effects on SV fusion. Molecular dynamics simulations indicate these mutations alter the topology of the C2B Ca2+ binding pocket and disrupt Ca2+-triggered membrane insertion. Several mutations outside of this region acted through a gain-of-function mechanism to enhance neurotransmitter release, while others caused the protein to undergo degradation. Consistent with this latter subset acting via haploinsufficiency, heterozygotes lacking one copy of SYT1 displayed a [~]40% decrease in evoked release. These data indicate C2B Ca2+ binding pocket mutations act dominantly to poison the fusion machinery and block release sites, while mutations outside of this region cause haploinsufficiency or gain-of-function effects with milder effects on synaptic output and behavioral phenotypes.

neuroscience↗

bioRxiv2026

Liquid liquid phase separation of the intrinsically disordered protein JPT2compartmentalizes components of NAADP-evoked Ca2+ signaling

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a Ca2+-releasing second messenger that activates two-pore channels (TPCs) on endosomes and lysosomes. Rather than binding TPCs directly, NAADP acts through cytoplasmic NAADP-binding proteins (NAADP-BPs) which are essential for endolysosomal Ca2+ release. Here we characterized the properties of two recombinant, purified NAADP-BPs: Jupiter Microtubule Associated Homolog 2 (JPT2) and like-Sm protein 12 (LSM12). In contrast to LSM12, JPT2 is predicted to be an intrinsically disordered protein, a feature confirmed by circular dichroism and NMR spectroscopy. Under conditions of low Na+ concentration or molecular crowding, JPT2 underwent phase separation, as demonstrated by multiple orthogonal approaches. JPT2 condensates displayed liquid-like behavior and efficiently recruited LSM12, a novel fluorescent NAADP analog, as well as tubulin. JPT2 condensates also interacted with polymerized microtubules and lysosomes isolated from human cell lines. These findings reveal an unexpected capability of NAADP-BPs to undergo phase separation, and segregate with components needed for NAADP-dependent Ca2+ release. We speculate that these signaling condensates dictate cellular NAADP sensitivity, desensitization of NAADP responses, as well as NAADP targeting to TPCs at membrane contact sites between acidic organelles and the endoplasmic reticulum. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/698830v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@108ebc4org.highwire.dtl.DTLVardef@ae9eb9org.highwire.dtl.DTLVardef@36b859org.highwire.dtl.DTLVardef@81053a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2026

Lab-on-a-3D-Printer for Democratized Reconfigurable Digital Microfluidics

Automation in the life sciences remains dominated by expensive, centralized robotic systems, leaving most laboratories unable to access precision robotic liquid handling. Here we present the Lab-on-a-3D-Printer (Lo3DP), a reconfigurable robotic microfluidic platform that repurposes the motion control, thermal regulation, and open-source programmability of consumer 3D printers to deliver laboratory-grade automation at a hardware cost below $500. By replacing the extruder with a multifunctional magnetic toolhead, Lo3DP actuates ferrofluid droplets with sub-100 {micro}m positioning accuracy and programmable volume control spanning 0.5-25 {micro}L, enabling the full repertoire of digital microfluidic operations within inexpensive laser-cut chips (<$3). We quantitatively validate system performance through long-term droplet transport exceeding 40,000 s without degradation, automated serial dilutions with high linearity (R{superscript 2} [≥] 0.99), and fully automated colorimetric nucleic acid amplification assays whose results match conventional benchtop workflows under tightly regulated isothermal conditions (CV {approx} 0.3%). By harnessing the global economies of scale of consumer 3D printers, Lo3DP provides accurate, reproducible, and programmable assay automation at a fraction of the cost and footprint of conventional systems, establishing a practical path toward desktop-scale, democratized laboratory robotics.

bioengineering↗

bioRxiv2025

Synthesis of perfluorooctanoic acid-containing membrane lipids by human pathobionts

Per- and polyfluoroalkyl substances (PFAS) are synthetic fluorinated compounds used widely in industrial and consumer products. They are unusually stable due to carbon-fluorine bonds and resistant to degradation, making them persistent contaminants in water, soil, and biota. PFAS are associated with adverse health effects in humans including cancer and liver disease. The effects of PFAS on human-associated bacteria are largely unexplored, a significant gap in knowledge because these bacteria are exposed to PFAS in vivo at sites including the colon and bladder. One of the best studied PFAS compounds is perfluorooctanoic acid (PFOA), an eight-carbon perfluorinated carboxylic acid whose structure is analogous to a fatty acid. Here, we cultured Enterococcus faecalis, a Gram-positive bacterium, and Pseudomonas aeruginosa, a Gram-negative bacterium, in growth medium supplemented with PFOA and corresponding control conditions and performed lipidomic analyses using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to elucidate lipid remodeling in response to PFOA exposure. Strikingly, novel fluoroalkyl-containing membrane lipids are synthesized by both of these bacteria, with each species synthesizing unique fluoroalkyl-lipids. Moreover, a high-level daptomycin-resistant strain of E. faecalis produces strikingly high levels of fluoroalkyl-lipids, demonstrating that prior antibiotic exposure and concomitant effects on bacterial evolution can alter bacterial interactions with PFAS. Because bacterial lipids are important immunomodulators in vivo, we propose that PFAS-containing bacterial lipids may be novel mediators of host-microbe-pollutant interactions. Our results also establish a novel mechanism for the bioaccumulation of PFOA and, potentially, for bioremediation of PFOA in biological systems such as the human gastrointestinal tract.

microbiology↗

bioRxiv2025

Transcriptional and epigenetic repression of hematopoietic stem cells underlies bone marrow failure after spinal cord injury

Spinal cord injury (SCI) triggers systemic pathology beyond the nervous system, including bone marrow failure that can worsen infection risk, anemia, and motor recovery. Here we identify a neuroendocrine mechanism that rapidly imprints long-lasting dysfunction in hematopoietic stem cells (HSCs), which sustain lifelong production of immune cells, red blood cells, and platelets. Rather than mounting a canonical stress-hematopoietic response, SCI HSCs enter a broadly repressed state marked by chromatin closure and suppression of programs required for cell-cycle entry, genome maintenance, and redox defense. This maladaptive state leads to persistent DNA damage, impaired oxidative stress resolution, pancytopenia, and loss of long-term HSC regenerative capacity. Mechanistically, SCI-induced glucocorticoid surges drive glucocorticoid receptor-dependent repression of DNA repair genes, including Lig1 and Fen1. Acute glucocorticoid receptor blockade after SCI restores durable hematopoiesis, revealing an early therapeutic window to preserve hematopoietic integrity after neurotrauma. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/680535v2_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1627bb3org.highwire.dtl.DTLVardef@a73e19org.highwire.dtl.DTLVardef@1ddf85dorg.highwire.dtl.DTLVardef@1dcd8fe_HPS_FORMAT_FIGEXP M_FIG C_FIG Key FindingsO_LIAcute SCI prevents induction of normal stress-induced repair programs in HSCs. C_LIO_LISCI HSPCs exhibit increased chromatin compaction. C_LIO_LISCI compromises HSC genome-maintenance and redox capabilities. C_LIO_LISCI HSCs have defects in normal cell cycle regulation, are hypersensitive to genotoxic stress, and are deficient in long-term reconstitution. C_LIO_LIEarly glucocorticoid receptor (GR) blockade restores long-term hematopoiesis, supporting a GR-dependent but reversible repression mechanism. C_LI

cell biology↗

bioRxiv2025

CpgD is a phosphoglycerate cytidylyltransferase required for ceramide diphosphoglycerate synthesis

Lipopolysaccharide (LPS) is essential in most Gram-negative bacteria, but mutants of several species have been isolated that can survive in its absence. Caulobacter crescentus viability in the absence of LPS is partially dependent on the anionic sphingolipid ceramide diphosphoglycerate (CPG2). Genetic analyses showed that ccna_01210, which encodes a nucleotidyltransferase, is required for CPG2 production. Using purified recombinant protein, we determined that CCNA_01210 (CpgD) is a phosphoglycerate cytidylyltransferase which uses CTP and 3-phosphoglycerate to produce CDP-glycerate, which we hypothesize is the phosphoglycerate donor for CPG2 synthesis. CpgD had optimum activity at pH 7.5-8 in the presence of magnesium. CpgD exhibited Michaelis-Menten kinetics with respect to 3-phosphoglycerate (Km,app = 10.9 {+/-} 0.7 mM; Vmax,app = 0.72 {+/-} 0.02 {micro}mol/min/mg enzyme) and CTP (Km,app = 4.8 {+/-} 0.9 mM; Vmax,app = 0.44 {+/-} 0.03 {micro}mol/min/mg enzyme). The characterization of this enzyme uncovers another piece of the pathway towards CPG2 synthesis.

biochemistry↗

bioRxiv2024

Vibrio cholerae O1 El Tor A1552 encodes two functional ornithine lipid synthases and induces ornithine lipid formation under low phosphate and under low salinity growth conditions.

Ornithine lipids (OLs) are phosphorus-free membrane lipids that can be formed by a wide range of bacteria. The presence of OLs is frequently related to the resistance to abiotic stress conditions, and its synthesis is often induced as part of various stress responses. Two different pathways for synthesizing OLs are currently known: the OlsBA pathway first described in Sinorhizobium meliloti, and the OlsF pathway first described in Serratia proteamaculans. We identified in the genome of Vibrio cholerae O1 El Tor A1552 two genes encoding OlsF homologs, VC0489 is located on chromosome 1, whereas VCA0646 is located on chromosome 2. Both synthases, when expressed in Escherichia coli, caused the synthesis of OLs. Single mutants deficient in each of the OL synthases, double mutants deficient in both OL synthases, and mutants deficient in the transcriptional regulator PhoB were constructed and characterized. We corroborated that VC0489 is solely responsible for the synthesis of OLs under phosphate-limitation. The deletion of VC0489 reduced the growth velocity compared to the wildtype under phosphate-limiting conditions but not under phosphate-replete conditions. The expression of VCA0646 is favored under low salt growth conditions, and its deletion abrogates OL synthesis at low salinities. The absence of VCA0646 and, therefore, the lack of OLs under low salt conditions makes the respective mutant more susceptible to polymyxin than OL-forming strains. None of the mutants was affected in biofilm formation, swimming, or virulence assays using Caenorhabditis elegans or Galleria mellonella. Here, we describe two functional OL synthases present in a single bacterium for the first time, and we show evidence that OLs have an important function during the V. cholerae lifecycle.

microbiology↗

bioRxiv2024

mTOR inhibition alleviated tau phosphorylation-induced mitochondrial impairment, oxidative stress, and cognitive impairment

AimHyperphosphorylated tau is a hallmark of Alzheimers disease (AD). However, whether mammalian target of rapamycin (mTOR) directly regulates tau phosphorylation at Ser214, Ser356, and Thr231 and how such regulation affects mitochondrial function remain unclear. In this study, we aimed to determine whether mTOR-mediated tau phosphorylation disrupts mitochondrial and metabolic profiles and cognitive function and whether these effects can be reversed by the mTOR inhibitor rapamycin. MethodsTau3E-overexpressing mice were generated by bilateral injection of adeno-associated virus vectors encoding the phosphomimetic TauS214E/T231E/S356E (Tau3E) variant into the hippocampal CA3 region of 2-month-old C57BL/6 mice. The mice received intraperitoneal rapamycin for one week. Cognitive performance was assessed using the Morris water maze. MALDI-mass spectrometry imaging was conducted to evaluate metabolic alterations in the brain tissue slices. mTOR, p70S6K, and tau phosphorylation protein expression; mitochondrial dynamics markers; and reactive oxygen species (ROS) levels were analyzed by Western blotting, immunofluorescence, and flow cytometry in HT22 cells, Tau3E mice, and postmortem AD brain tissues. ResultsPhosphorylated mTORS2448 colocalized with p-TauSer214, p-TauSer356, and p-TauThr231 in the hippocampal CA3 region of AD brains. HT22 cells and Tau3E mice exhibited increased levels of p-mTOR, p-p70S6K, and ROS production; mitochondrial fragmentation; and tau phosphorylation at Ser214, Ser356, and Thr231. Rapamycin treatment partially ameliorated cognitive deficits, reduced oxidative stress and mitochondrial dysfunction, and restored metabolic profile particularly the inosine-pentose phosphate pathway-glycolysis metabolic axis, structural lipidome axis and the neurotransmitter homeostasis. ConclusionmTOR activation contributes to site-specific tau hyperphosphorylation, mitochondrial dysfunction, and cognitive impairment. Pharmacological inhibition of mTOR by rapamycin attenuated tau pathology, regulated metabolic alterations, preserved mitochondrial homeostasis, and improved cognitive function, suggesting a potential therapeutic strategy for AD.

neuroscience↗

bioRxiv2024

Orexinergic projections to substantia innominata mediate arousal and analgesia

Understanding neural circuits involved in anesthesia is crucial for improving its safety and efficacy. Hypothalamic orexin neurons (LHAOX), projecting broadly, are essential in regulating arousal and pain. However, the precise targets remain unclear. Here we investigated the orexin projections to the substantia innominata (SI). Combining optogenetics, fiber photometry, and EEG/EMG allowed us to manipulate orexin activities, while simultaneously recording local ligand release and global cortical activities during anesthesia. Brain slice electrophysiology revealed the synaptic connections in the SI, while RNAscope was employed to examine the distribution of orexin receptors and downstream neuronal types. Presynaptic vesicles were identified in the orexin terminals in the SI, where 49.16% of cells expressed OX2R and 6.8% expressed OX1R. Orexin release in the SI was reversibly suppressed by isoflurane. Optogenetic activation of the LHAOX[->]SI circuit significantly increased orexin release and promoted arousal from various anesthesia stages, including reanimation during 0.75% isoflurane (p < 0.0001), prolongation of 3% isoflurane induction (p = 0.0033), and acceleration of emergence from 2% isoflurane (p < 0.0001). Furthermore, activating this circuit induced analgesia to both thermal (p = 0.0074) and inflammatory (p = 0.0127) pain. Patch-clamp recordings revealed that optogenetic activation of orexin terminals in the SI elicited excitatory postsynaptic currents, which were blocked by the OX2R antagonist. SI contains more GABAergic (28.17%) and glutamatergic (11.96%) neurons than cholinergic neurons (4.13%), all of which expressed OX2R. Thus, LHAOX neurons innervate SI neurons to regulate both arousal and pain predominantly through OX2R.

neuroscience↗

bioRxiv2024

Biosynthesis of mitis group streptococcal glycolipids and their roles in physiology and antibiotic susceptibility

Bacterial cell surface components such as lipoteichoic acids (LTAs) play critical roles in host-microbe interactions and alter host responses based on their chemical structures. Mitis group streptococci have commensal and pathogenic interactions with the human host and produce Type IV LTAs that are slightly different in chemical structures between species. To reveal the molecular bases for the intricate interactions between MGS and human hosts, a detailed understanding of the structure and biosynthetic process of MGS LTAs is needed. In this study, we used genomic and lipidomic techniques to elucidate the biosynthetic processes of Type IV LTA and its associated glycolipid anchors, monohexosyl-diacylglycerol and dihexosyl-diacyglycerol, in the infectious endocarditis isolate Streptococcus sp. strain 1643. Through establishing a murine sepsis model, we validated the essentiality of these glycolipids in the full virulence of S. mitis. Additionally, we found that these glycolipids play an important role in protecting the bacteria from antimicrobials. Overall, results obtained through this study both confirm and dispute aspects of the existing model of glycolipids biosynthesis, provide insights into the fundamental roles of bacterial glycolipids, as well as suggest the potential of targeting glycolipids for developing antimicrobial therapeutics. Significance/ImportanceGlycolipids and glycolipid-anchored LTAs are common and essential membrane components in Gram-positive bacteria. Yet, the biosynthesis and functions of LTAs have not been fully understood for many significant Gram-positive pathogens. Through genomic, lipidomic, and animal infection model analyses, as well as antimicrobial susceptibility assays, this study advances our understanding of Type IV LTA biosynthesis and the physiological roles of glycolipids in mitis group streptococci. Overall, our work establishes the essentiality of glycolipids in both bacterial virulence and defense against antimicrobials.

microbiology↗